Interfacial processes for the polymerization of polycarbonate yield a mixture comprising an aqueous phase and an organic phase. The aqueous phase, also referred to as the brine phase, comprises salts, ionic species, and interfacial catalyst. The organic phase, also referred to as the polymer phase, comprises solvent, dissolved polycarbonate, and interfacial catalyst. Some salts or ionic species (hereinafter “ions” for convenience) can further be present in the organic phase as a result of brine entrainment from the aqueous phase. These ions, as well as any interfacial catalyst, are generally removed from the organic phase in a purification process as they affect the final product quality. The purification process generally involves separation of the aqueous phase from the organic phase followed by the removal of ions and catalyst in one or more extraction steps to result in a purified polycarbonate.
A problem in polycarbonate purification processes is that the organic phase and the aqueous phase can form an emulsion, especially in the manufacture of copolycarbonates and polycarbonate-esters. Emulsification is characterized by creation of small, difficult-to-remove droplets of a first phase dispersed within a second phase. Accordingly, emulsification can result in one or both of only a partial separation of the organic and the aqueous phase, such that part of the organic phase is carried over and flows out with the aqueous phase; and an insufficient removal of impurities (such as ions and catalyst) from the organic phase. As a result, stable plant operation can be difficult to maintain and ultimately the quantity and the quality of the purified polycarbonate can be reduced.
A purification process that treats a removed aqueous phase comprising organic phase carryover to further separate out the polycarbonate carryover is desirable.